1. Field of the Invention
The present invention relates to pumps and, more particularly, relates to centrifugal pumps particularly well suited for reliably pumping liquids containing solid materials without damaging the pump or causing excessive pump repairs.
2. Description of the Prior Art
Centrifugal pumps have long been used and are preferred in many applications for moving liquids under pressure. U.S. Pat. No. 745,857 discloses a rotary pump having outer and inner walls which draws liquid through an axially aligned inlet, and discharges liquid from a tangential outlet. Centrifugal pumps, as disclosed in U.S. Pat. No. 2,348,246, typically include rotary vanes intended for 37 wiping" the surrounding pump walls to move fluid through the pump. Other types of centrifugal pumps are disclosed in U.S. Pat. Nos. 2,581,055, 3,095,821, and 3,272,129. A backward-inclined impeller for a centrifugal pump is disclosed in U.S. Pat. No. 4,666,373.
Special problems are understandably encountered when using a centrifugal pump to pump liquids containing a high percentage of solids. A centrifugal pump particularly designed for handling sewage which contains solid objects is disclosed in U.S. Pat. No. 3,130,678. A similar pump with improved non-clogging characteristics intended for handling sewage is disclosed in U.S. Pat. No. 3,295,456. A mixed flow "trash pump" with a resilient liner is disclosed in U.S. Pat. No. 4,419,048. This latter pump is particularly designed for handling water which contains silt, sand, or other abrasive materials. A pump with impeller vanes having a leading edge behind a flange with cutting edge grooves is disclosed in U.S. Pat. No. 4,594,052, such that the leading edge of the vane and the cutting edge grooves detach and shred fibers and sticks in the liquid. This design allegedly prevents these solid objects from accumulating, and prevents the objects from being conveyed into a slot between the vane and the housing.
In spite of these attempts, prior art centrifugal pumps still are frequently not able to reliably handle liquids containing solid objects. Pumps frequently become plugged with solids and/or the solid objects become jammed between the pump housing and the impeller. Moreover, repair costs for prior art centrifugal pumps used to handle liquids with solid objects is extremely high.
In an attempt to minimize the problems associated with prior art centrifugal pumps intended for handling fluids with solid objects, pumps have been devised wherein the impellers are functionally out of the flow path of the fluid. U.S. Pat. No. 2,958,293, for example, discloses a pump with an impeller which is substantially removed from the flow path of the fluid. The stated objective of such a pump is to minimize or reduce jamming or clogging of the pump in response to solid particles, and to reduce repair and maintenance on the pump. A similar type of pump useful for pumping fluids with solid materials is disclosed in U.S. Pat. No. 4,575,308. A significant problem with these latter types of pumps, however, is that the pumps deliver a relatively low pressure head to the fluid, so that the pump with a conventionally sized motor cannot be successfully used to pump fluids over a large distance. The efficiency of the pump under high pressure is so poor that the pump cannot be practically used in many applications where the fluid which contains the solid material must be pumped vertically a distance of 20 feet or more.
The disadvantages of the prior art are overcome by the present invention, and an improved centrifugal pump is hereinafter disclosed which is particularly suitable for pumping liquids containing solid materials which have heretofore caused plugging, jamming, or excessive repair to prior art pumps.